UV-curable coatings were developed many years ago. Many products make use of UV-cured coatings because such coatings are functional (tough, abrasion resistant, stain resistant, water resistant); and attractive (high gloss, endless color selection) and manufacturing friendly (fast curing, inexpensive light source, minimum space requirements). Because of their versatility, UV-curable coatings, in the form of inks, are working their way into the digital printing environment. However, UV-curable coatings and inks come with a unique set of problems that have already been solved for conventional inks and coatings. Until now, UV-curable fluids have typically been used only with piezoelectric ejection heads. Such piezoelectric ejection heads are generally more costly than thermal ejection heads and are typically provided separate from the ink supplies making maintenance of the ejection heads more difficult and costly.
By way of further background, thermal inkjet devices ejecting conventional, i.e., non-UV-curable inks, typically use inks consisting of 70-80 wt. % water. The remaining mass fraction is typically made up of high boiling point co-solvent/humectants, colorant-dispersants, surfactants and biocides. Conventional inks are formulated for use on paper and other substantially porous or ink absorbing substances. While paper is ubiquitous, there is a significant need for inks that can print on a wider variety of surfaces—in particular non-porous surfaces such as plastic, metal, and glass. It is known that UV-curable inks and coatings are particularly suitable for applying to non-porous surfaces. However, UV-curable inks and coatings are generally solvent based formulations, wherein the solvent is generally selected from ethanol, methanol, I-propanol, or similar low boiling point liquids.
There are several disadvantages to the use of solvent-based inks and coatings. For one, because of the increased low boiling solvent content in the UV-curable inks and coatings, the ejection kinetics, particularly in the case of thermal micro-fluid ejection devices is significantly lower than aqueous-based inks and coatings. Secondly, solvent based inks and coatings are much more hazardous and pose more danger to the environment than aqueous-based inks and coatings.
Another problem with the use of UV-curable inks and coatings is that the fluids cure when exposed to light. While this is desirable when the fluids are to be cured on a surface, curing of such fluids on the surfaces of the ejection devices or in the ejection nozzles may cause misfiring and other unwanted results. Accordingly, there is a need for UV-curable formulations and micro-fluid ejection devices that provide suitable coating performance in a more environmentally acceptable way. There is also a need for a micro-fluid ejection device that can be operated efficiently to provide high quality images and coatings made from UV-curable fluids.
In view of the foregoing, embodiments of the disclosure provide methods, apparatus, and compositions that are suitable for applying UV-curable fluids via micro-fluid ejection devices. In one embodiment, there is provided a UV-curable fluid composition that is suitable for ejection using a micro-fluid ejection device.
In another embodiment, there is provided a thermal micro-fluid ejection head for ejecting a UV-curable fluid onto a surface. The ejection head includes a nozzle plate having a radiation opaque coating thereon for preventing premature curing of the fluid.
Another embodiment of the disclosure provides a method for operating a thermal micro-fluid ejection head for applying a UV-curable fluid to a substrate.
Yet another embodiment of the disclosure provides a method for coating a surface with a UV-curable fluid to provide a high resolution image on the surface.
Another embodiment of the disclosure provides a page-wide device for applying a UV-curable coating to a substrate.
Still another embodiment of the disclosure provides a scanning micro-fluid ejection head device for applying a UV-curable coating to a substrate.
An advantage of embodiments of the disclosure may be minimal nozzle plate flooding thereby greatly improving droplet ejection directionality and droplet placement on a substrate. Aqueous UV-curable fluids, as described herein, provide a fire frequency that is 40% less than a fire frequency of a conventional aqueous-based ink composition. The fire frequency is lower because the UV-curable fluids generally have higher viscosity than traditional aqueous-based inks thereby reducing the refill rate to fluid ejection chambers. In other words, the micro-fluid ejection system ejecting a UV-curable fluid is more damped than a system operating on a conventional aqueous-based ink. However, despite the lower fire frequency, the UV-curable fluid may actually have no negative impact on throughput of imaged substrates because of minimal flooding, straighter droplet directionality, better droplet placement, and fewer shingling passes needed to provide an image.